Method of manufacturing a flexible pipe

ABSTRACT

A flexible pipe comprises an inner supporting pipe (1) made from an elastic material, onto which inner supporting pipe a shaped strip (2) is wound. Said strip (2) has a cross-section profile formed by two stepwise conjugated quadrangular flanges (3) and (4), the height of each of the flanges being equal to a half of the height of the profile. The adjacent turns of the strip (2) partially overlap each other so that the upper flange (3) of one turn is superimposed onto the lower flange (4) of the other flange, and the ends of the flanges (3) and (4) are aligned. An interlayer (5) made from an elastic material is superimposed onto the power frame formed by the strip (2). At least one pair of reinforcing layers (6) and (7) formed by groups of power filaments (8) and (9) is disposed on said interlayer (5), said filaments being parallel to one another and wound in contrary at angles of from 0° to 20° to the axis of the pipe. A protective shell (10) made from an elastic material is superimposed onto the pair of the reinforcing layers (8) and (9). A method of manufacturing a modification of a flexible pipe having an interlayer (5) with a helical expansion (15) comprises the steps of: superimposing a shaped strip (2) onto the inner supporting pipe (1). Said strip (2) is fixed to the supporting pipe (1), whereupon the pipe is stretched along the axis thereof. Then the power frame formed by the strip (2) is covered with the interlayer (5) from an elastic material and fixed to the strip (2). Thereafter, the reinforcing layers (6) and (7) are wound, the protective shell is superimposed thereon, and the supporting pipe (1) is released from the action of the axial tensile load.

This is a division of application Ser. No. 261,206, filed 5/12/81, nowU.S. Pat. No. 4,403,631, issued 9/13/83.

TECHNICAL FIELD

The present invention relates to the design of machine components,namely to flexible pipes and to methods of making same.

The inventive flexible pipe may prove most advantageous in feedingworking media under conditions characterized by the effect of increasedinternal and external loads, e.g. in petroleum, gas, coal, and chemicalbranches of industry as well as in aerospace technology and in offshorehydraulic structures.

Among the above loads are primarily an axial force, gage internal orexternal pressure, and torque. It is important that a flexible pipe doesnot change its cross-section shape, preserve its flexibility under theaction of such loads, and be light, simple and cheap in manufacture.

The problem of developing such flexible pipes had become urgentcomparatively long time ago in aeronautics and in offshore technology.Attention is being given to this problem recently as a result ofcarrying out space experiments and developing the continental shelf.

Analysis of prior art technical solutions demonstrates that this problemhas not been satisfactorily solved up to now.

BACKGROUND ART

Known in the art is a flexible pipe whose design makes it possible totransmit working media under increased pressure and at the same time toreceive an axial tensile force (French Pat. No. 2,142,764). Saidflexible pipe comprises a rubber supporting pipe onto which pipe severallayers of metal braid are wound in spiral. The lowest layer and theuppermost layer are wound with a shift in the winding angles of from 6°to 80°. Metal wires in all the layers are subject to tension and allowthe flexible pipe cross-section to be preserved at a slight bendingthereof under conditions of simultaneous influence of gage internalpressure and a slight axial tensile force.

However, such a flexible pipe cannot be applied in the case of effect ofdistributed or local external load, e.g. under the influence of gageexternal pressure. Under the effect of compression in the radialdirection, the cross-section of the flexible pipe loses its stabilitydue to the fact that the metal wires constituting the braid cannotresist this effect.

Also known in the art is a flexible pipe which is intended to receive,without deformation, apart from gage internal pressure and an axialtensile force, gage external pressure (USSR Inventor's Certificate No.668,625). In accordance with the above disclosure, this flexible pipecomprises an inner supporting pipe constructed from an elastic materialonto which pipe a flat strip from a rigid material (e.g. metal) iswound. The above strip forms a cylindrical power casing with aninterlayer from an elastic material being put thereupon. Two layers ofshaped rods are wound in crossed directions onto said interlayer. Thecross-section of each rod has a maximum size in the radial direction.Said rods are wound symmetrically at angles of up to 40°.

Undoubtedly, the presence of the rods wound at such angles will allowthe flexible pipe to receive an axial tensile force and gage internalpressure without fracture. However, if such a flexible pipe is placedinto a medium whose pressure exceeds the pressure within the flexiblepipe, the deformation of the flexible pipe becomes possible even at thepressure drop of 4 to 5 kg/cm², said deformation being accompanied bythe loss in stability of its cross-section. This is due to the fact thatthe pressure of the external medium is freely transmitted through thegaps between the shaped rods (especially under tension) to theinterlayer made from an elastic material and, correspondingly, to thepower frame formed by the flat strip. The rigidity of this frame in theradial direction is low and is in no way reinforced by the shaped rodswhich are by themselves subject only to tension. Thus, the power frame,after having lost its stability, will be locally pressed into theflexible pipe. Simultaneously, the turns of the flat strip willseparate, and the tightness of the flexible pipe will be certainlyupset. Naturally, the above shortcomings will take place only atdifferentials in internal and external pressure of more than 4 to 5kg/cm².

To our opinion, the most successful is a construction of a flexible pipedeveloped by the company "Coflexip S.A." (see advertising brochure"Coflexip flexible pipe for the offshore industry" by this company,published in 1979). The above flexible pipe comprises an innersupporting pipe constructed from an elastic material, a shaped striphaving a Z-shaped cross-section and wound in a spiral onto said pipe.The Z-shaped cross-section of the strip is formed by two stepwiseconjugated parallel flanges. The upper and the lower flanges areconjugated therebetween by means of a leg. Each flange is constructed inthe form of an angle and rests by the edge of this angle on the oppositeflange of the next turn of the strip. Thickness of each flange issubstantially less (5 to 10 times) than the height of the strip profile.The above design is substantially one of modifications of the inventionof a S-shaped profile. Thus, said angles of adjacent turns of a stripare put into engagement and limit the possibility of extending the powerframe formed by the strip, in the axial direction. An interlayer of anelastic material is superimposed onto the power frame formed by a shapedstrip. On the interlayer, there is provided at least one pair ofreinforcing layers formed by groups of power filaments, said groupsbeing parallel to one another, and wound substantially in a symmetricalposition. The power filaments are provided in the form of steel wiresand are wound at angles of 40° to 60° to the axis of the flexible pipe.The flexible pipe is also provided with an external protective shellmade from an elastic material.

An obvious advantage of the above described construction of the flexiblepipe consists in that such a design makes it possible to receive threetypes of loads: an axial tensile force, gage internal pressure, and gageexternal pressure. A sufficiently good perception of the gage externalpressure is promoted by the fact that the strip forming the power frameis made in the shaped form, and all the structure of the flexible pipeis hermetically sealed by the external protective shell. Whilepossessing the above advantages, the flexible pipe can maintain itsflexibility.

Nevertheless, in the manufacture of such a flexible pipe it is necessaryto utilize such expensive and high quality materials as alloy steels,titanium etc. Such a need is caused by the following considerations: acomparatively small thickness of flanges is required to provide forreliable engagement between the angles thereof because with the abovementioned angles of winding the power filaments, the latter do notensure the complete perception of the total axial tensile force.Therefore, to avoid distortion of uniformity of the power frame (i.e. toeliminate the possibility of formation of through gaps between the stripturns under tension), the presence of engaging angles is necessary. Forthis reason, and also due to a rather complex technology of stripshaping, reinforcement of said strip by increasing the thickness of theflanges is impracticable. Moreover, the upper flange of each turn of thestrip rests on the lower flange of the adjacent turn with acomparatively narrow edge of the angle. Consequently, the material fromwhich the shaped strip is constructed, must possess highphysico-mechanical properties, including high hardness among them. Itwill be understood that in order to reinforce the power frame, the powerfilaments of the reinforcing layers are also to be constructed from ahigh-strength steel wire. It should be also noted that the strength ofthe power frame receiving a portion of the axial tensile force isdetermined essentially by the strength of the weakest joint between twoadjacent turns of the strip. The above consideration imposes especiallyhigh demands upon the production process of the shaped strip and theframe.

Disclosure of the Invention

The principal object of the present invention is to provide a hose inwhich the structure of reinforcing layers and the construction of aframe allow inexpensive materials to be used for the manufacture of thesame hose without reducing its strength. The object set forth isattained by that in the flexible pipe comprising an inner supportingpipe made from an elastic material; a power frame formed by a shapedstrip having a Z-shaped cross-section with two stepwise conjugatedflanges, the strip being wound in a spiral fashion onto the supportingpipe in such a way that the upper flange of each turn is disposed overthe lower flange of the adjacent turn, an interlayer made from anelastic material and superimposed onto the power frame, at least onepair of reinforcing layers formed by groups of power filaments, saidfilaments being parallel to one another and wound in contrary onto saidinterlayer; and an external protective shell made from an elasticmaterial, according to the invention, each of said flanges is of aquadrangular cross-section and is of a height equal to one half of theheight of the profile of the strip so that the upper flange of each turnrests directly on the lower flange of the adjacent turn, and the ends ofthe upper flanges as well as the ends of the lower flanges are aligned,the power filaments of each reinforcing layer being wound at angles offrom 0° to 20° to the axis of the pipe.

It turned out that with such a construction of the flexible pipe all theaxial tensile force is received by the power filaments constituting thereinforcing layers. Therefore, there is no need in any angles engagingthe turns of the shaped strip and limiting mutual displacement of theseturns in the axial direction. Thus, elimination of the effect of theaxial tensile load upon the power frame made it possible to get rid ofthe most vulnerable link represented by the angles engaging the turns ofthe strip therebetween. This has resulted in a considerablesimplification of the production process of the shaped strip and hasprovided for a possibility of manufacturing said strip from suchinexpensive materials as low-carbon structural and tool steels.Consequently, there are no conditions for the local wear of the strip asit took place in the prior art construction. The same factor makes itpossible to substantially lower such a requirement placed upon thematerial as hardness thereof. Combination of the above characteristicsmakes it possible to increase durability and reliability of the flexiblepipe, and to considerably lower its cost.

In the construction of a flexible pipe intended for operation underconditions of constant effect of the dynamic axial tensile load, theinterlayer from an elastic material is expedient to have a helicalexpansion disposed above the butt formed between the ends of the upperflanges of the strip turns.

With sudden application of the axial tensile force, the supporting pipeand the interlayer are deformed first, the helical expansion isstraightened out, and only then the power filaments get strained andcome into operation.

For operation at very large depths, such a modification of the flexiblepipe is advisable wherein between the power frame and the lowerreinforcing layer of the power filaments wound at angles of 0° to 20°,there is provided at least one layer of a similar shaped strip wound inthe opposite direction.

A modification of the flexible pipe is preferred, wherein between theinterlayer from an elastic material and a pair of reinforcing layers ofthe power filaments wound at angles of 0° to 20°, there is provided alayer formed by the power filaments wound at an angle of 30° to 60° tothe axis of the flexible pipe.

It turned out that with such a construction the flexible pipe canreceive a torque and an axial compression force. Rigidity of theflexible pipe is proportional to the magnitude of the torque. Powerfilaments wound at an angle of 30° to 60° increase their angle ofwinding under the effect of such loads and squeeze the power frame whileshifting the turns of the strip and thereby making said frame rigid andstrong.

To ensure joint operation of all the layers and to eliminate thepossibility of wearing-through the power filaments, it is expedient thatthe layer formed by said power filaments wound at an angle of 30° to 60°be closed by an additional interlayer from an elastic material.

The widest performance possibilities has a modification of the flexiblepipe wherein on the ends of the flanges of the shaped strip there areprovided longitudinal projections and grooves being congruent thereto,into which grooves said projections enter when the turns of the stripare brought together. Such a flexible pipe possesses flexibility both inunloaded state and under the effect of an axial tensile load. However,under the effect either of an axial compression force, or of a torque,the flexible pipe is transformed into a rigid pipe. The projections andthe grooves provided at the ends of the flanges, ensure reliableengagement between the turns.

It is expedient that the flanges forming the profile of the stripcross-section, have a form of parallelograms. In this case the ends ofthe flanges in the strip turns have a conical shape, thereby ensuringself-alignment of the turns being brought together.

The same effect is achieved in a modification of the flexible pipewherein the ends of the flanges having the cross-section in the form ofa parallelogram, are rounded and have similar curvature radii. Roundingsof the ends impart the flexible pipe an increased flexibility in theunloaded state.

The object set forth is also attained by that there is provided a methodfor manufacturing a flexible pipe, comprising the steps of superimposinga shaped strip preliminarily bent in a spiral, onto an inner supportingpipe, covering the power frame formed by the shaped strip, with aninterlayer from an elastic material with simultaneous fastening saidinterlayer to the strip; winding reinforcing layers, and superimposingan external protective shell, wherein, according to the invention, priorto covering the power frame with the interlayer, the internal supportingpipe is fixed to the shaped strip, stretched along the axis thereof, andafter superimposing the external protective shell is released from theaction of the axial tensile load.

This makes it possible to wind reinforcing layers onto a smoothcylindrical surface of a blank of the interlayer, while the spiralexpansion on said interlayer is formed after releasing the supportingpipe the axial tensile force.

It should be noted that the supporting pipe is returned into the initialstate without formation of any crimps or wrinkles on the surfacethereof.

BRIEF DESCRIPTION OF DRAWINGS

The invention is further explained in more detail in terms ofdescription of the flexible pipe and a process for manufacturing samewith reference to the accompanying drawings, in which:

FIG. 1 shows the flexible pipe of the present invention in a partialaxial cross-section;

FIG. 2 shows a cross-sectional view of a fragment of the supporting pipeand the power frame formed by the shaped strip;

FIG. 3 shows a modification of the flexible pipe, reinforced to receivean internal gage pressure;

FIG. 4 shows a modification of the flexible pipe provided according tothe invention with a shaped elastic interlayer;

FIG. 5 shows an axial cross-sectional view of a fragment of thesupporting pipe, the power frame and the shaped interlayer in astretched state prior to vulcanization;

FIG. 6 shows the fragment illustrated in FIG. 5 when the flexible pipeis in a free state;

FIG. 7 shows a modification of the flexible pipe having a power frameformed according to the invention by two layers of shaped strips;

FIG. 8 shows a modification of the flexible pipe having according to theinvention with an additional reinforcing layer;

FIG. 9 shows an enlarged fragment of the supporting pipe and of theshaped strip provided according to the invention with projections andgrooves;

FIG. 10 shows a modification of the shaped strip provided with flangeshaving a cross-section in the form of a parallelogram according to theinvention;

FIG. 11 shows a modification of the flexible pipe, similar to thatillustrated in FIG. 11 but with rounded ends of the flanges according tothe invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The flexible pipe of the present invention comprises an inner supportingpipe 1 (FIG. 1) constructed from an elastic material. Such elastomers asrubber, natural and synthetic rubbers, polyamides, polyurethane etc. canbe utilized as the elastic material. A shaped strip 2 is wound in spiralonto the supporting pipe 1, said strip being constructed from aresilient material having a modulus of elasticity within the range of6×10⁴ to 4×5.10⁶ kg/cm². In particular, the strip 2 can be constructedfrom metals and alloys thereof, and from some rigid plastics such aspolypropylene etc.

The shaped strip 2 is wound at an angle to the axis of the flexiblepipe, which angle is within the range of 60° to 85°. The strip 2 has aZ-shaped cross-sectional configuration formed by two stepwise conjugatedflanges 3 and 4 being of a quadrangular cross-section. The height ofeach of the flanges 3 and 4 is equal to one half the height h of theprofile of the strip 2 (FIG. 2). The shaped strip 2 is wound in such amanner that adjacent turns partially overlap one another as it can beseen in FIGS. 1 and 2 of the accompanying drawings. The upper flange 3of each turn of the strip 2 rests on the lower flange 4 of the adjacentturn of the strip 2. The ends of the upper flanges 3 as well as the endsof the lower flanges 4 of the adjacent turns of the strip 2 are aligned.Thus, spirally wound shaped strip 2 forms a cylindrical power frameallowing the flexible pipe to preserve its cross-sectional shape whenbending, and also under the effect of considerable radial loads, e.g.internal or external gage pressure.

An interlayer 5 constructed from an elastic material is superimposedonto the power frame formed by the shaped strip 2. Onto the interlayer 5there is wound at least one pair of reinforcing layers 6 and 7. Thereinforcing layer 6 is formed by a group of power filaments 8 which areparallel to one another. The power filaments 8 are wound at an angle αto the axis of the flexible pipe. The angle α is selected within therange of 0° to 20°. The second reinforcing layer 7 is wound in thecounter direction to the layer 6. This layer 7 is formed by a group ofpower filaments 9 which are parallel to one another. The power filaments9 are wound at an angle α₁ to the axis of the flexible pipe. The angleα₁ is equal to the angle α and is also selected within the range of 0°to 20°.

An external protective shell 10 is superimposed onto the reinforcinglayer 7. Said shell 10 is constructed from an elastic material.

It will be understood that apart from the above described components,the inventive flexible pipe may comprise other flexible reinforcingcomponents as well. The number of the reinforcing layers is alsounlimited. For example, FIG. 3 illustrates a modification of theflexible pipe which is reinforced to receive internal gage pressure.According to this modification, between the interlayer 5 and thereinforcing layer 6 there are symmetrically wound two additionalreinforcing layers 11 and 12. The additional reinforcing layers 11 and12 are formed by respective groups of power filaments, 13 and 14respectively, the filaments of each group being parallel to one another.The power filaments 13 and 14 are wound at angles β and β₁ to the axisof the flexible pipe. The values of the angles β and β₁ are equal to oneanother and are selected within the range of 75° to 90°.

The interlayer 5 superimposed onto the shaped strip 2, can be of aconstant thickness over the whole length of the flexible pipe. However,more preferred is a modification of the flexible pipe illustrated inFIG. 4. According to this modification, the interlayer 5 constructedfrom an elastic material, has a helical expansion 15 disposed above thebutt or gap between the adjacent ends of the upper flanges 3 of theadjacent turns of the shaped strip 2.

In FIG. 6 of the accompanying drawings the shape of the expansion 15 ofthe interlayer 5 and location of said expansion are shown in moredetail.

In the process of developing the given modification, it appeared thatwith prior art methods it is impossible to provide a spiral expansion 15on the elastic interlayer 5, said expansion being located exactly overthe butt or gap between the adjacent ends of the upper flanges 3 of thestrip 2. It should be also noted that even a slight shift of theexpansion 15 relative to the butt will offset the effect obtained withthe help of said expansion. Moreover, it is impracticable to uniformlywind the power filaments 8 and 9 (FIG. 4) onto the interlayer 5 providedwith the expansion 15. For this reason, there has been concurrentlydeveloped a method of manufacturing the modification of the flexiblepipe illustrated in FIG. 4.

The method comprises the following consequently accomplished steps.According to the invention, a strip 2 which has been preliminarily bentin a spiral shape is put on the inner supporting pipe 1. Said strip 2 issecured to the supporting pipe 1 following which the supporting pipe 1is stretched along the axis thereof. A tubular blank 16 constructed froman elastic material (FIG. 5) is superimposed onto the power frame formedby the shaped strip 2. The tubular blank 16 is fixed to the shaped strip2. The walls of the tubular blank 16 are of a constant thickness overthe whole length of the flexible pipe. The reinforcing layers 6 and 7(FIG. 4) are wound onto the tubular blank 16. Following this, theprotective external shell is superimposed, and the flexible pipe isheated to soften the elastic material, and to impart required mechanicalproperties to this material (e.g. to vulcanize rubber). Then thesupporting pipe 1 and the power frame formed by the strip 2, arereleased from the effect of an axial tensile load. Under the action ofresilient forces, the supporting pipe 1 and the power frame return totheir initial state. The pitch of winding of the shaped strip 2 isreduced, thereby reducing gaps between the ends of its upper flanges 3.Thus, the tubular blank 16 being rigidly connected with the strip 2 getscompressed and a spiral expansion 15 is formed thereon, said expansionfilling the gap between the ends of the upper flanges 3 (FIG. 6 of theaccompanying drawings). The spiral expansion 15 locates without failexactly above the butt or gap between the ends of the upper flanges 3 ofthe turns of the strip 2.

The power frame can be formed not only by one layer of the shaped strip2. The number of such layers may be two or more. If the power frame isformed by at least two layers of the shaped strips 2 and 17 (FIG. 7),the strips 2 and 17 are wound in opposite directions. If the power frameis formed by a greater number of layers, the layers in the adjacentlayers are wound in opposite directions.

Now consider the modification of the flexible pipe illustrated in FIG.8. As it can be seen in this figure, the given modification comprisesall the elements of the flexible pipe shown in FIG. 1. Thedistinguishing feature of this modification consists in that a layer 18is provided between the interlayer 5 and the pair of reinforcing layers6 and 7 of the power filaments 8 and 9. The layer 18 is formed by powerfilaments 19 which are parallel to one another and wound at an angle γto the axis of the flexible pipe. The angle γ is selected within therange of 30° to 60°. Said layer 18, according to the invention, isclosed by an additional interlayer 20 constructed from an elasticmaterial, the reinforcing layer 6 being wound directly onto saidinterlayer.

The modification of the flexible pipe shown in FIG. 9 possesses thewidest performance possibilities. According to this modification, on theends of the flanges 3 and 4 of the shaped strip 2, there are providedlongitudinal projections 21 and grooves 22 being congruent thereto. Itwill be understood that both the projection 21 and the groove 22 can beof various cross-sections (e.g. rectangular). The main conditiondetermining the shape of the cross-section either of the projection 21or of the groove 22, is the provision of the possibility of free entryof the projections 21 into the grooves 22 when the turns of the shapedstrip 2 are brought together.

The same possibility is ensured by the modification of the shaped strip2 illustrated in FIG. 10. In accordance with this modification, theupper flanges 3 and the lower flanges 4 forming the profile of thecross-section of the strip 2, have the form of a parallelogram. Thus,sharpened ends of the flanges 3 and 4 are substantially the projections21, while the grooves 22 are defined by sharpened ends of the lowerflanges 4 and by the supporting pipe 1, and also by sharpened ends ofthe upper flanges 3 and the surfaces of the lower flanges 4 beingadjacent thereto.

The ends of the flanges 3 and 4 are not necessarily flat but can be alsoformed by curvilinear surfaces. For example, FIG. 11 illustrates themodification of the shaped strip 2 provided with rounded ends of theflanges 3 and 4. The flanges 3 and 4 have the form of parallelograms andare so constructed that the radii of curvature of their ends are equalone another.

In transportation of the working medium under the effect of internal andexternal loads, the above described flexible pipe operates as follows.

The modification of the flexible pipe shown in FIG. 1 of theaccompanying drawings, can be utilized under conditions characterized bysimultaneous or alternate effects of such factors as gage internal andexternal pressure, and an axial tensile load. Under such conditions, theflexible pipe preserves its flexibility both in working and in idlestates. The axial tensile force is substantially received by the powerfilaments 8 and 9 of the reinforcing layers 6 and 7. The shape of thecross-section of the flexible pipe under the effect of gage externalpressure and in bending, is preserved due to the presence of the powercylindrical frame formed by the shaped frame 2.

In bending the flexible pipe, the gap provided within the butt or gapbetween the upper flanges 3 is increased on one side of the flexiblepipe, while on the other side said gap is reduced. That is, on thesurface of a greater bending radius of the flexible pipe, the turns ofthe shaped strip 2 are brought apart (but continue to partially overlapone another), while on the surface of a smaller bending radius saidturns are brought together. The power filaments 8 and 9 of thereinforcing layers 6 and 7 prevent an exceeding emergency increase inthe gap within the butt between the upper flanges 3. Since thesefilaments 8 and 9 are wound at an angle from 0° to 20° to the axis ofthe flexible pipe, and are rather rigid in the axial direction, theyprovide for flexibility of the pipe while limiting the possibility ofits elongation. Gage internal pressure is received by the supportingpipe 1, which pipe while being deformed, transmits this pressure to thepower frame formed by the shaped strip 2. Since the power frame iscovered with the reinforcing layers 6 and 7 of the power filaments 8 and9, the flexible pipe preserves its cross-sectional shape.

The modification of the flexible pipe shown in FIG. 3 can withstandconsiderably greater gage internal pressure. In this case the majorportion of the radial load occurring under the action of gage internalpressure is received by the power filaments 13 and 14 of the additionalreinforcing layers 11 and 12.

The modification of the flexible pipe shown in FIG. 4 while preservingall the advantages of the above described modifications, allows dynamicloads (e.g. axial jerks, hydraulic impacts etc.) to be damped. Indynamic loading such a flexible pipe by an axial tensile force, at firstthe supporting pipe 1, the interlayer 5, and the external protectiveshell 10 constructed from an elastic material, start to becomeresiliently deformed. In the course of deformation, the energy of theaxial loading is partially absorbed. As the process of axial deformationproceeds, the spiral expansion 15 of the interlayer 5 vanishes, thepower filaments 8 and 9 straighten out and start receiving the majorportion of the axial tensile load. Thus, the reinforcing layers 6 and 7come into operation constantly under the dynamic axial load, therebysignificantly increasing reliability and durability of the flexiblepipe.

The modification of the flexible pipe shown in FIG. 7 operatessubstantially as above described under stretching, and under the actionof internal and external gage pressure, though external or internal gagepressure is received successfully not only by the shaped strip 2, butalso by a layer formed by an analogous shaped strip 17. The aboveconsideration makes it possible to use the given modification of theflexible pipe under considerably more severe conditions, e.g. whenoperating at large depths.

The modification of the flexible pipe shown in FIG. 8 allows not onlyaxial stretching, external and internal gage pressure to be received,but also compression in the axial direction, and a torque.

Consequently, the above modification of the flexible pipe is capable ofpreserving stability under the action of axial compression, i.e. it canpresent a rigid pipe at the same time, be a flexible pipe in the absenceof a torque and of an axial compression load. Such a feature is attainedby the presence of a reinforcing layer 18 whose power filaments 19 arewound at an angle of 30° to 60° to the axis of the flexible pipe.

In the absence of an external load, availability of gaps between theadjacent edges of the upper flanges 3 of the shaped strip 2 provides forflexibility of the flexible pipe. Thus, the flexible pipe can be storedand shipped wound on a drum. When receiving internal and external gagepressure, and an axial tensile load, the above modification of theflexible pipe functions substantially as above described. When theflexible pipe is compressed in the axial direction, the upper flanges 3of the turns of the shaped strip 2 are brought together, the gap betweenthe flanges 3 disappears, and the angle of winding the power filaments19 increases approaching the upper limit thereof, i.e. 60°. This resultsin that the flexible pipe transforms into a rigid structure. Similarcompression of the flexible pipe in the axial direction also occurs whenapplying a torque thereto. Under the action of the torque, the angle ofwinding the power filaments 19 increases. The reinforcing layer 18squeezes the power frame formed by the shaped strip 2, thereby promotingan increase in rigidity and stability thereof. It is apparent that thegreater is the value of the torque, the higher is rigidity and stabilityof the flexible pipe.

The modification of the flexible pipe illustrated in FIGS. 9 through 11of the accompanying drawings, possesses significantly higher rigidityand stability.

Under axial compression, and under the effect of a torque, the turns ofthe shaped strip 2 are brought together. The projections 21 enter thegrooves 22, thereby limiting the freedom of relative displacement of theturns of the strip 2 in the radial direction. Thereby stability of theflexible pipe is substantially increased. The above advantages allow thegiven modification of the flexible pipe to be used as drilling pipes.Relative alignment of the turns of the shaped strip 2 under the actionof axial compression is promoted by the shape of the flanges 3 and 4illustrated in FIGS. 10 and 11. In these cases, the projections 21 andthe grooves 22 have the form of a cone and that of a convex body ofrevolution, which factor will result in an inevitable alignment of theturns of the strip 2 when the above turns are brought together.

Industrial Applicability

The flexible pipe of the present invention can be used for feedingworking media under conditions characterized by the effect of increasedinternal and external loads. Most advantageously the flexible pipe canbe used in petroleum, gas, coal, and chemical branches of industry aswell as in aerospace technology and in offshore hydraulic structures.

While the invention has been described herein in terms of specificembodiments thereof, numerous variations and modifications may be madein the invention without departing from the invention as set forth inthe appended claims.

We claim:
 1. A method for manufacturing a flexible pipe comprising aninner supporting pipe made from an elastic material, a power frameformed by a shaped strip having a Z-shaped cross-sectional profile withtwo stepwise conjugated flanges, the strip being wound in a spiralfashion onto the supporting pipe such that the upper flange of each turnis disposed over the lower flange of the adjacent turn, an interlayerformed of an elastic material and superimposed onto the power frame, atleast one pair of reinforcing layers including an upper and a lowerlayer, said reinforcing layers being formed by groups of powerfilaments, said filaments being parallel to one another and wound inopposed directions onto said interlayer, and an external protectiveshell formed of an elastic material, wherein each of said flanges is ofa quadrangular cross-section and is of a height equal to one half of theheight of the profile of the strip so that the upper flange of each turnrests directly on the lower flange of the adjacent turn, and the ends ofthe upper flanges as well as the ends of the lower flanges are aligned,the power filaments of each reinforcing layer being wound at angles offrom about 0° to 20° to the axis of the pipe and wherein said interlayeris made from an elastic material and has a helical expansion disposedabove the butt formed between the ends of the upper flanges of the turnsof the strip, comprising the steps of superimposing said shaped strip,preliminarily bent in a spiral onto an inner supporting pipe defining apower frame on said support tube with said upper flange of each turn ofsaid spiral disposed over said lower flange of the adjacent turn, andsaid lower flange being fixed to said support pipe, tensioning saidpower frame and said support tube to longitudinally stretch same,covering the longitudinally stretched power frame formed by the shapedstrip with an interlayer of an elastic material with simultaneousfastening of said interlayer to the strip, winding on saidlongitudinally stretched power frame each of said groups of powerfilaments in opposite directions to form reinforcing layers, andsuperimposing an external protective shell, over said reinforcinglayers, and releasing said tension to allow said stretched power frameand support tube to contract and compress said elastic interlayer.